Easy Build FM Transmitter
This is a low cost and easy build low powered FM transmitter. The range of the FM transmitter claimed about 300 feets when running at 9V supply. And the range claimed to be increased become about 400 feet when running it at 12V supply. Take a note that this transmitter should not be used as a room or telephone bug.
C1 = 1nF
C2 = 5.6pF
C3,C4 = 10uF/16V
C5 = 3-18pF Varco/Varicap
R1 = 270 Ohm 1/4W
R2,R5,R6 = 4.7K 1/4W
R3 = 10K 1/4W
R4 = 100K 1/4W
Q1, Q2 = 2N2222A or 2N3904 or NTE123A
L1, L2 = 5 Turn Air Core Coil
MIC = Electret Microphone
MISC : 9V Battery Snap, PC Board, Wire For Antenna
FM transmitter circuit notes:
- L1 and L2 are 5 turns of 28 AWG enamel coated magnet wire wound with a inside diameter of about 4mm. The inside of a ballpoint pen works well (the plastic tube that holds the ink). Remove the form after winding then install the coil on the circuit board, being careful not to bend it.
- C5 is used for tuning. This transmitter operates on the normal broadcast frequencies (88-108MHz).
- You may want to bypass the battery with a .01uF capacitor.
- An antenna may not be required for operation.
FM Transmitter circuit source: http://www.aaroncake.net/circuits/fmtrans.asp